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UD scientists help build neutrino telescope in Antarctica

NEWARK, DE.--Working under harsh Antarctic conditions, an international team of scientists led by the University of Wisconsin-Madison and including researchers from the University of Delaware, has set in place the first critical elements of a massive neutrino telescope at the South Pole.

The successful deployment in a 1.5 mile-deep hole drilled into the Antarctic ice of a string of 60 optical detectors designed to sample phantom-like high-energy particles from deep space represents a key first step in the construction of the $272 million telescope known as IceCube. The project also includes an array of detectors on the surface, known as IceTop, for which the University of Delaware is the lead institution.

The telescope and its construction are being financed by the National Science Foundation (NSF), which will provide $242 million. An additional $30 million in support will come from foreign partners.

“It’s all on track,” according to Francis Halzen, a University of Wisconsin-Madison professor of physics and the principal investigator for the project. “This was our first exam. We met our milestones for the season, and we can move on to the next Antarctic summer.”

"We successfully installed four surface stations," Thomas K. Gaisser, Martin A. Pomerantz Chair of Physics and Astronomy at UD’s Bartol Research Institute, said. Each station consists of two tanks of ice viewed by the same optical modules used in the deep detector, according to Gaisser.

Serap Tilav, a Bartol scientist who returned Friday from Antarctica, reported that IceTop is taking data. “The 16 IceTop optical modules are presently initiating the trigger of the string of detectors deep in the ice,” she said.

In an announcement Tuesday, Feb. 15, scientists and managers of the project declared a successful first season of construction of what will become the world’s largest scientific instrument.

Halzen said building the telescope requires drilling at least 70 one-and-one-half-mile-deep holes in the Antarctic ice using a novel hot-water drill, and then lowering long strings of volleyball-sized optical detectors--4,200 in all--into the holes where they will be frozen in place. The 140 IceTop tanks will contain an additional 280 detectors.

The first string, with 60 detectors, was successfully lowered into the ice in late January, and communication with the detectors, each of which is like a small computer, has been successfully established.

When completed, the telescope will use a cubic kilometer of Antarctic ice as a detector and will be capable of capturing information-laden, high-energy particles from some of the most distant and violent events in the universe. It promises a new window to the heavens and may be astronomy’s best bet to resolve the century-old quest to identify the sources of cosmic rays.

The IceCube telescope will look for the telltale signatures of high-energy cosmic neutrinos, ghostlike particles produced in violent cosmic events­colliding galaxies, distant black holes, quasars and other phenomena occurring at the very margins of the universe. Cosmic rays, which are composed of protons, are thought to be generated by these same events. But, protons are bent by the magnetic fields of interstellar space, preventing scientists from following them back to their points of origin.

Cosmic neutrinos, on the other hand, have the unique ability to travel cosmological distances without being absorbed or deflected by the stars, galaxies and interstellar magnetic fields that permeate space. Their ability to skip through matter without missing a beat promises unedited information about the early universe and the very violent objects that populate deep space.

Thomas K. Gaisser, Martin A. Pomerantz Chair of Physics and Astronomy at UD’s Bartol Research Institute, at work on an IceTop optical module in Antarctica. Photo courtesy of the University of Wisconsin-Madison
But, that same phantom-like property--the ability to travel billions of light years and pass unhindered through planets, stars and galaxies--makes detecting cosmic neutrinos extraordinarily difficult.

"Neutrinos travel like bullets through a rainstorm," Halzen explained. "Immense instruments are required to find neutrinos in sufficient numbers to trace their origin."

The optical modules that make up the detector act like light bulbs in reverse. They are able to sense the fleeting flash of light created when neutrinos passing through the Earth from the Northern Hemisphere occasionally collide with other atoms. The subatomic wreck creates another particle called a muon. The muon leaves a trail of blue light in its wake that allows scientists to trace its direction, back to a point of origin, potentially identifying the cosmic accelerators--black holes or crashing galaxies, for example--that produce the high-energy neutrinos.

The IceTop surface array “will detect and study events produced by high-energy cosmic-ray particles interacting in the atmosphere above IceCube,” Gaisser said. “Such downward events produce the main background in the deep neutrino telescope so tagging them with the surface array will improve the signal to background ratio of the instrument. Events detected in coincidence by both the surface and the deep detectors also carry information about the origin of the cosmic rays of very high energy. This information will be complementary to that obtained from the upward events in the neutrino telescope.”

The telescope now under construction at the South Pole is an international effort involving more than 20 institutions. The project is funded by NSF, with significant contributions from Germany, Sweden, Belgium, Japan, New Zealand, the Netherlands and the Wisconsin Alumni Research Foundation.

In the U.S., the project involves scientists from University of Wisconsin-Madison and the University of Delaware, as well as from the University of California at Berkeley, the Lawrence Berkeley National Laboratory, the University of Maryland, Penn State University, the University of Wisconsin-River Falls, the University of Kansas, the University of Alabama, Clark Atlanta University, Southern University and A&M College and Princeton University’s Institute for Advanced Study.

This year marks the first year of work on the IceCube telescope, which is being built around a much smaller neutrino telescope known as AMANDA for Antarctic Muon and Neutrino Detector Array.

?We’ve had an extremely productive year,? Jim Yeck, the IceCube project director, said. Accomplishments include fabrication of telescope instrumentation at collaborating institutions, shipping almost 1 million pounds of cargo to the South Pole, assembly and successful operation of the custom-built hot water drill, installation of facilities and instrumentation on the ice and setting the first IceCube string into the ice.

Yeck added that undertakings like the IceCube neutrino observatory and other polar science projects by U.S. researchers would not be possible without the strong logistics and science support provided by Raytheon Polar Services Co., the NSF’s prime support contractor in Antarctica, and without the strong support of the New York Air National Guard, which provides air cargo and delivery of personnel, and the U.S. Coast Guard, which keeps sea lanes open to the U.S. Antarctic coastal bases.

“If we stay on schedule, IceCube could take over next year as the world’s largest neutrino telescope,” Halzen said.

Several representatives of Bartol were at the South Pole in November and December working on the project. Joining Gaisser were Paul Evenson, professor of physics, and James Roth, senior electronics specialist. Tilav was at the South Pole during January and early February.

Also working on the IceTop project from Bartol are David Seckel, associate professor of physics; Todor Stanev, professor of physics; senior scientist John Clem; scientists Stoyan Stoyanov and Xinhua Bai; researchers Peter Niessen and Tonio Hauschildt; and graduate students Divya Swarnkar and Nehar Arora.

Article by Neil Thomas

Photos by Kathy F. Atkinson